Former student is depressed, missing girl in opening (7)

I believe the answer is:

alumnus

I'm a little stuck... Click here to teach me more about this clue!

'former student' is the definition.
(I've seen this before)

'depressed missing girl in opening' is the wordplay.
'depressed missing girl' becomes 'lum' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'opening' becomes 'anus' (anus is a kind of opening).
'lum' inserted into 'anus' is 'ALUMNUS'.

'is' acts as a link.

Can you help me to learn more?

(Other definitions for alumnus that I've seen before include "(US) college graduate" , "School or college graduate" , "Past pupil" , "Former college pupil" , "Former school pupil" .)

I've seen this clue in The Hindu.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.